Film formation mask

ABSTRACT

Provided is a film formation mask capable of preventing slit-like openings from being closed by vibrations so as to form a highly precise patterned film with stability. In a film formation mask formed by providing multiple slit-like openings in a metal foil, the shape of the opening of at least one end of the slit-like openings is asymmetrical with respect to a center line of the width direction of the slit-like openings.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a film formation mask for highlyprecise pattering, in which slit-like openings are provided in a metalfoil, and more particularly, to a film formation mask for use in a vapordeposition process of an organic material in manufacturing an organicelectroluminescence display device.

2. Description of the Related Art

In manufacturing an organic electroluminescence (EL) display device, asa process of forming an organic compound layer, there is known a methodof forming a pattern of an organic material by using a film formationmask in which openings are provided in a metal foil. In this method, athin film is formed by causing a vapor deposition material which haspassed through the openings in the film formation mask to reach asubstrate. This method is widely used, because a pattern of an organicfilm may be formed without using lithography. In recent years, a moreand more finer pixel pattern is required. Thus, as the film formationmask, a tension mask is widely used, in which a thin metal foil having ahighly precise opening pattern formed therein is attached to a frame. Inparticular, a slit-like opening pattern is widely used from theviewpoint of the ratio of area of openings in the mask and openings in apixel.

For example, Japanese Patent No. 4,173,722 discloses a film formationmask having an ordinary slit-like opening pattern formed therein. Inthis film formation mask, the lengths, the shapes, and the pitches ofthe slit-like openings are uniform and the ends of the openings arealigned, and thus, the shapes and the positions of the metal foilbetween the openings are the same. Japanese Patent Application Laid-OpenNo. 2007-234678 discloses a film formation mask in which the ends ofslit-like openings are gradually tapered toward the tips. Also in thiscase, the lengths, the shapes, and the pitches of the slit-like openingsare uniform and the ends of the openings are aligned, and thus, theshapes and the positions of the metal foil between the openings are thesame. Further, Japanese Patent Application Laid-Open No. 2003-332059discloses a mask having bridges formed between openings. The ends ofodd-numbered columns of openings and the ends of even-numbered columnsof openings are staggered, and thus, the mask is less liable to bedeformed by tension applied to the film formation mask and is highlyprecise, which improves the precision of the vapor deposition film.

A film formation mask having a fine opening pattern in which multipleslit-like openings are arranged has a problem that the sides of metalfoil portions provided on both sides of the slit-like opening in a shortside direction thereof are brought into contact with each other byvibrations. Such vibrations are caused when the film formation mask isbrought into contact with a glass substrate or when the film formationmask is peeled off in a film formation process, or, when the mask istransferred. When such contact is caused, the slit-like openings arepartly closed, and as a result, a problem arises that a film formationpattern in a desired shape cannot be formed. In particular, when theamount of an organic material deposited on the film formation maskincreases, the state in which the sides of the metal foil portions arein contact with each other is maintained by the organic materialdeposited on the mask, and hence the area of closed portions of theslit-like openings increases.

Further, in the film formation mask disclosed in Japanese PatentApplication Laid-Open No. 2003-332059, vibrations of the metal foilportions are scarcely caused by external vibrations because the bridgesare formed, and thus, the above-mentioned problem that the slit-likeopenings are closed does not arise. However, the ratio of the area ofthe openings becomes smaller, and thus, the aperture ratio of a pixelbecomes smaller with respect to the mask. When light is emitted with thesame luminance, an increase in power consumption or a decrease in lifeis caused.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to solve theabove-mentioned problems and to provide a film formation mask havingmultiple slit-like openings formed therein, which is capable ofpreventing the slit-like openings from being closed by vibrations, so asto form a highly precise patterned film with stability.

According to the present invention, there is provided a film formationmask, including a metal foil fixed to a frame body with stronger tensionapplied to the metal foil in one direction than in another direction, inwhich:

the metal foil includes slit-like openings elongated in the onedirection, which are repeatedly provided in a short side direction ofthe slit-like openings; and

a shape of at least one end of each of the slit-like openings isasymmetrical with respect to a center line of a short side of theslit-like openings.

According to the present invention, the slit-like openings of the maskare prevented from being closed by vibrations. Therefore, by using themask according to the present invention, a finely shaped pattern may berepeatedly obtained with high precision. In particular, in manufacturingan organic EL display device, a highly precise organic compound layermay be formed with high precision, and the yield and manufacturingefficiency may be improved.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are an overall schematic view, a partially enlargedschematic view, and a sectional view, respectively, of a film formationmask according to an embodiment of the present invention.

FIG. 2 is an enlarged schematic view of an end of a slit-like opening ofthe film formation mask illustrated in FIG. 1B.

FIG. 3A is a schematic view illustrating movement of metal foil portionsdue to vibrations of a conventional film formation mask, and FIG. 3B isa schematic view illustrating movement of metal foil portions due tovibrations of the film formation mask according to the presentinvention.

FIG. 4 is a schematic view illustrating a shape of the slit-likeopenings of the film formation mask of an example according to thepresent invention.

FIG. 5 is a schematic view illustrating a shape of the slit-likeopenings of the film formation mask of another example according to thepresent invention.

FIG. 6 is a schematic view illustrating a shape of the slit-likeopenings of the film formation mask of a comparative example of thepresent invention.

FIGS. 7A, 7B, 7C and 7D are explanatory diagrams of how a slit-likeopening in a conventional film formation mask is closed.

FIG. 8 is a schematic view illustrating an organic EL display deviceaccording to the present invention.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

A film formation mask according to the present invention has, basically,similarly to a conventional mask, a structure in which a metal foilhaving multiple slit-like openings formed therein is fixed to a framebody under tension. The multiple slit-like openings provided in themetal foil are in a pattern in which openings having the same shape arerepeatedly provided in parallel shift in a short side direction of theopenings. The tension applied to the metal foil is stronger in a longside direction of the openings than in the short side direction of theopenings. Conventionally, ends of the slit-like openings are symmetricalwith respect to a center line of the short side of each of the openings,but, according to the present invention, ends of the slit-like openingsare asymmetrical.

In the following, an embodiment of the film formation mask according tothe present invention is described. It is to be noted that well-known orpublicly known technologies in the art may be applied to parts which arenot specifically illustrated or described herein. Further, theembodiment described in the following is merely an embodiment of thepresent invention, and the present invention is not limited thereto.

FIGS. 1A to 1C illustrate an exemplary film formation mask according tothe present invention. FIG. 1A is a plan view of the whole filmformation mask, FIG. 1B is an enlarged schematic view of a regiondenoted as 3 of FIG. 1A, and FIG. 1C is a sectional view taken along theline 1C-1C of FIG. 1A. FIGS. 1A to 1C illustrate a film formation mask1, patterned openings 2, slit-like openings 4, ends 5 of the slit-likeopenings, a metal foil portion 6, a metal foil 8, a frame body 9 forfixing the metal foil thereto, and a region D which corresponds to onedisplay panel. In the present invention, the metal foil as a whole whichis fixed to the frame body 9 is referred to as the metal foil 8, and ametal foil between the slit-like openings is referred to as the metalfoil portion 6, so as to be distinguished from each other. The length ofarrows in FIGS. 3A and 3B represents the magnitude of tension applied tothe metal foil. FIG. 2 is an enlarged view of one end 5 of the slit-likeopening 4 illustrated in FIG. 1B. According to the present invention, asillustrated in FIG. 2, the shape of the opening of at least one end 5 ofthe slit-like opening 4 is asymmetrical with respect to a center line Oof the short side of the slit-like opening 4 (in a horizontal directionof the sheet of the drawings). It is preferred that, as illustrated inFIG. 2, the shapes of the openings of both ends 5 be asymmetrical withrespect to the center line O of the short side, and in addition, asillustrated in FIG. 1B, be symmetrical with respect to a center line Pof the long side of each of the slits. According to the presentinvention, the shape of the opening of the end 5 is made asymmetricalwith respect to the center line O of the short side as illustrated inFIG. 2, to thereby prevent the slit-like opening 4 from being closed.The reason is described in the following.

FIGS. 7A and 7C are plan views schematically illustrating a conventionalfilm formation mask. FIG. 7B is a sectional view taken along the line7B-7B of FIG. 7A, while FIG. 7D is a sectional view taken along the line7D-7D of FIG. 7C. FIGS. 7A and 7B illustrate a state of the mask beforefilm formation, and FIGS. 7C and 7D illustrate a state in which aslit-like opening 4 is closed. Also in the conventional mask, strongtension is applied to the metal foil portions 6 in the long sidedirection of the slit-like openings, but the metal foil portions 6 mayvibrate to both sides in the short side direction of the slit-likeopenings 4 (to the right and to the left in the sheet of the drawings).Therefore, when a metal foil portion 6 vibrates with an amplitude of atleast half the short side of the slit-like opening 4, as illustrated inFIGS. 7C and 7D, the sides of the metal foil portions 6 provided on bothsides of the slit-like opening 4 may be brought into contact with eachother to partially close the slit-like opening 4.

Next, tension (stress) applied to the metal foil portion 6 whenvibrations are caused is described with reference to FIGS. 3A and 3B.FIG. 3A is a schematic plan view partially illustrating the metal foil 8including multiple openings in the conventional film formation mask,which is also illustrated in FIGS. 7A to 7D, and FIG. 3B is a schematicplan view partially illustrating the metal foil 8 including multipleopenings in the film formation mask according to the present invention.In the conventional film formation mask, the shape of the ends of theslit-like openings 4 is symmetrical with respect to the center line O ofthe short side. Therefore, as illustrated in FIG. 3A, stress 7 isuniformly applied to the metal foil portions 6 sandwiched betweenadjacent slit-like openings 4 both in the long side direction and in theshort side direction of the slit-like openings 4. Therefore, the metalfoil portion 6 uniformly vibrates in the width direction of theslit-like openings 4 (to the right and to the left in the sheet of thedrawings). On this occasion, when adjacent metal foil portions 6 vibratewith an amplitude of ½ of the width of the openings of the slit-likeopenings 4, the sides of the metal foil portions 6 provided on bothsides of the slit-like opening 4 are brought into contact with eachother, as described with reference to FIGS. 7C and 7D.

When the shapes of the ends of the slit-like openings 4 are asymmetricalwith respect to the center line O of the short side, as illustrated inFIG. 3B, the stress 7 applied to the metal foil portions 6 sandwichedbetween adjacent slit-like openings 4 is one-sided in the short sidedirection, and the direction of the vibrations of the metal foilportions 6 is limited to one side. Therefore, even when vibrations withan amplitude of ½ of the width of the openings of the slit-like openings4 are caused, the metal foil portions 6 provided on both sides of theslit-like opening 4 vibrate always in the same direction, and thus, thesides of the metal foil portions 6 are not brought into contact witheach other. Therefore, the slit-like openings 4 are prevented from beingclosed.

The film formation mask according to the present invention is preferablyused in manufacturing an organic electroluminescence (EL) displaydevice. An organic EL display device has, between a pair of electrodes,multiple organic EL elements each including an organic compound layer.The film formation mask according to the present invention is used invapor deposition of the organic compound layer. The organic compoundlayer includes at least an emission layer, and in addition, a holeinjection layer, a hole transport layer, an electron transport layer,and an electron injection layer are appropriately used as necessary. Itis to be noted that the film formation mask according to the presentinvention may be preferably used in a film formation process other thanin manufacturing an organic EL display device.

Example 1

A multi film formation mask as illustrated in FIGS. 1A to 1C and FIG. 2was manufactured, for forming an organic compound layer in sixteen VGAorganic EL display devices at single film formation. Openings in thesame shape were repeatedly formed in the metal foil of the filmformation mask. The shapes of ends of the slit-like openings 4 wereasymmetrical with respect to the center line O of the short side andsymmetrical with respect to the center line P of the long side. Thethickness of the metal foil 8 was 40 μm, the length of the short side ofthe slit-like openings 4 was 40 μm, the length of the long side thereofwas 55 mm, and the pitches in the short side direction of the slit-likeopenings 4 (that is, the width of the metal foil portion 6) was 120 μm.

This mask was used to form an organic EL display device illustrated inFIG. 8. An organic compound layer of an organic EL element was formed ona circuit board 10 having circuits for driving the organic EL displaydevice formed on a glass substrate. On the circuit board, firstelectrodes 11 each formed of a metal layer of 10 μm×60 μm were arrangedso as to be 1,920×480 in a row direction and in a column direction,respectively, with 120 μm pitches both in the row direction and in thecolumn direction for the respective organic EL elements for emitting redlight (R), green light (G), and blue light (B).

After the openings in the film formation mask were aligned with thecolumns of the first electrodes, an emission layer 12 having a thicknessof 40 nm as the organic compound layer was formed in multiple stripes.After the same film formation mask was used to form the filmcontinuously on 100 circuit boards, the film formation mask was takenout of a film formation apparatus and observed. The observation showedno phenomenon that metal foil portions of the mask were brought intocontact with each other to close the slit-like openings. A filmformation mask having an opening for each organic EL display device wasused to form a transparent conductive layer as a second electrode 13 onthe circuit board on which the organic compound layer was formed. Thesecond electrode was formed as a film which communicated with themultiple organic EL elements. After that, a sealing layer having siliconnitride as a main component which communicated with the sixteen organicEL display devices was formed without using a mask, and then, thecircuit board was cut into pieces to obtain sixteen organic EL displaydevices from one substrate. Among the obtained organic EL displaydevices, 40 organic EL display devices were randomly sampled and thefilm formation pattern was observed. There were no traces of thephenomenon that metal foil portions of the mask were brought intocontact with each other to close the slit-like openings.

Example 2

As illustrated in FIG. 4, a mask was manufactured similarly to the caseof Example 1 except that the shape of one end of each of the openingswas asymmetrical with respect to the center line O of the short side andthe shape of the other end of each of the openings was symmetrical withrespect to the center line O of the short side (in other words, each ofthe openings was asymmetrical with respect the center line P of the longside).

This mask was used to form an organic compound layer of an organic ELelement similarly to the case of Example 1. After the same filmformation mask was used to form the film at a thickness of 40 nmcontinuously on 100 circuit boards, the film formation mask was takenout of the film formation apparatus and the openings were observed. Theobservation showed no phenomenon that metal foil portions of the maskwere brought into contact with each other to close the slit-likeopenings. Further, similarly to the case of Example 1, the filmformation pattern was observed. There were no traces of the phenomenonthat metal foil portions of the mask were brought into contact with eachother to close the slit-like openings.

Example 3

As illustrated in FIG. 5, a film formation mask was manufacturedsimilarly to the case of Example 1 except that in the slit-like openings4, the shapes of the ends of each of the openings were asymmetrical withrespect to the center line O of the short side and symmetrical withrespect to the center line P of the long side.

This film formation mask was used to form an organic compound layer ofan organic EL element on a glass substrate. After the film formationmask was used to form the film at a thickness of 40 nm continuously on100 circuit boards, the film formation mask was taken out of the filmformation apparatus and the film formation mask was observed. Theobservation showed no phenomenon that metal foil portions of the maskwere brought into contact with each other to close the slit-likeopenings. Further, the film formation pattern on the glass substrate wasobserved. There were no traces of the phenomenon that metal foilportions of the mask were brought into contact with each other to closethe slit-like openings.

Comparative Example

As illustrated in FIG. 6, a film formation mask was manufacturedsimilarly to the case of Example 1 except that in the slit-like openings4, the shapes of the ends of each of the openings were symmetrical withrespect to the center line O of the short side and symmetrical withrespect to the center line P of the long side.

This film formation mask was used to form an organic compound layer ofan organic EL element on a glass substrate. After the film formationmask was used to form the film at a thickness of 40 nm continuously on100 circuit boards, the film formation mask was taken out of the filmformation apparatus and the film formation mask was observed. Theobservation showed a phenomenon that metal foil portions of the maskwere brought into contact with each other to close the slit-likeopenings. Further, the film formation pattern on the glass substrate wasobserved and traces of the phenomenon that metal foil portions of themask were brought into contact with each other to close the slit-likeopenings were found. It was then confirmed that the film formationpattern was defective on the almost entire surface by the 50th circuitboard.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2010-182075, filed Aug. 17, 2010 and Japanese Patent Application No.2011-153633, filed Jul. 12, 2011 which are hereby incorporated byreference herein in their entirety.

1. A film formation mask, comprising a metal foil fixed to a frame bodywith stronger tension applied to the metal foil in one direction than inanother direction, wherein: the metal foil includes slit-like openingselongated in the one direction, which are repeatedly provided in a shortside direction of the slit-like openings; and a shape of at least oneend of each of the slit-like openings is asymmetrical with respect to acenter line of a short side of the slit-like openings.
 2. The filmformation mask according to claim 1, wherein shapes of both ends of theslit-like openings are asymmetrical with respect to the center line ofthe short side of the slit-like openings and symmetrical with respect toa center line of a long side of the slit-like openings.
 3. (canceled)